Magnetic squeeze film damper system for a gas turbine engine

ABSTRACT

A magnetic squeeze film damper system comprises a bearing assembly having an outer race with a first outer surface and a first inner surface and a bearing located along the first inner surface. The system further comprises a squeeze film damper housing having a second outer surface and a second inner surface that is contiguous with the first outer surface. A channel having a forward end and an aft end is defined within the housing along the second inner surface, the channel bordered by the first outer surface. The system further includes a first seal gland located along the forward end of the channel and a second seal gland located along the aft end of the channel. Both seal glands comprise a reservoir for holding a magneto-rheological fluid, the reservoir encased in an elastomer. At least one electromagnet is arranged in close proximity to each of the seal glands.

BACKGROUND

The present disclosure relates to devices and systems to addressstability and vibration issues associated with high-speed rotatingturbomachinery. More particularly, the present disclosure relates todevices and systems for addressing stability and vibration issuesassociated with gas turbine engines used in aircrafts, for example.

In gas turbine engines, maintaining operational clearances between thetips of rotating blades and the engine static structure and controllingvibration generated by the high speed rotating components are designcritical factors in gas turbine engine development. Maintainingoperational clearances between the tips of rotating blades and thestatic structure of the engine to reduce air leakage past the rotatingblades impacts the thermodynamic efficiency and specific fuelconsumption (SFC) of the engine.

Further, gas turbine engine shaft dynamics are critical, including theplacement of shaft critical speed in the optimal frequency range and therotor response to imbalance and transient excursions through criticalspeeds. The critical speed is usually controlled by adjusting thestiffness/flexibility of various components of the gas turbine engine,such as, for example, the shaft or shafts, the bearings, and the supportstructures. Moreover, rotating shafts in gas turbine engines can becomeabnormally unbalanced while operating. For example, a high pressureturbine shaft can become abnormally unbalanced after a turbine bladefailure.

Shaft response to imbalance and transient critical speed operation(i.e., vibration response) are controlled via damping. In gas turbineengines, damping and stiffness control are typically achieved usinghydraulic devices such as squeeze film dampers (SFD). In a gas turbineengine, the SFDs work in conjunction with and are typically contiguouswith the various bearing systems that support the rotating shafts of theengine. A squeeze film damper achieves both stiffness and damping byvirtue of the whirl motion of the shaft acting on the oil filled annulus(cavity) of the SFD.

However, both the stiffness and the damping coefficient achieved bytypical SFDs are non-linear with respect to the orbital displacement ofthe shaft. Also, the stiffness and damping coefficients are linked suchthat a modification to one impacts the other. Because current SFDsystems do not provide for variable control during operation, they arenot able to precisely locate and control response to critical speeds,since stiffness and damping are varied along with whirl displacement.Thus, a SFD/bearing assembly is designed to cover the widest range ofoperating conditions for a particular engine.

A SFD that offers varied control would provide improved rotor tipclearance control during maneuver loading situations by limiting how farthe bearing can move radially. Further, varied control damping will helpkeep tip clearances tight and reduce air leakage past the rotor bladesresulting in improved specific fuel consumption. There remains a need toimprove sealing of the SFD cavity to improve the reliability andconsistency of the damping characteristics of the SFD system.

SUMMARY OF INVENTION

The magnetic squeeze film damper system of the present disclosurecomprises a bearing assembly having an outer race with a first outersurface and a first inner surface. The bearing assembly includes abearing located along the first inner surface. The magnetic squeeze filmdamper system of the present disclosure further comprises a squeeze filmdamper housing, which includes a second outer surface and a second innersurface. The second inner surface of the housing is contiguous with thefirst outer surface of the bearing outer race. A channel for flowing afluid is defined within the housing along the second inner surface, thechannel bordered by the first outer surface of the bearing outer race.The channel further includes a forward end and an aft end.

The magnetic squeeze film damper system of the present disclosurefurther includes a first seal gland located along the forward end of thechannel and a second seal gland located along the aft end of thechannel. The first seal gland seals the forward end of the channel andthe second seal gland seals the aft end of the channel. The first sealgland comprises a reservoir encased by an elastomer. The reservoircontains a fluid having suspended metal particles, such as amagneto-rheological fluid. The second seal gland also comprises areservoir constructed to contain a magneto-rheological fluid. At leastone electromagnet is arranged in close proximity to each of the sealglands. The magnetic squeeze film damper system of the presentdisclosure also includes an electronic control system, which may includea current generator and various sensors to generate varied current toenergize the electromagnets.

DESCRIPTION OF THE FIGURES

FIG. 1 is a cross section of one aspect of the present disclosureshowing a magnetic squeeze film damper/bearing assembly supporting ashaft of a gas turbine engine.

FIG. 2 is an enlarged cross section of the relevant structure of themagnetic squeeze film damper/bearing assembly of FIG. 1.

FIG. 3 is a cross section of a two spool gas turbine engineincorporating the bearing assembly of FIGS. 1-2.

FIG. 4 is a cross section of a three spool gas turbine engineincorporating the bearing assembly of FIGS. 1-2.

FIG. 5 is a diagram of one aspect of the present disclosure showing oneembodiment of an electronic control system of the magnetic squeeze filmdamper.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the disclosure is therebyintended. It is further understood that the present disclosure includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles disclosed herein aswould normally occur to one skilled in the art to which this disclosurepertains.

Referring to FIG. 1 and FIG. 2, a non-limiting embodiment of the presentinvention is depicted. One embodiment of the present invention includesa bearing assembly 10 having an outer race 20. The outer race 20includes a first outer surface 30 and a first inner surface 40. Thebearing assembly includes at least one bearing 50 located along thefirst inner surface 40. The at least one bearing can be any type ofbearing suitable for use in a gas turbine engine to support a rotatableshaft of the engine. Such bearings can include roller bearings or ballbearings for radial load and thrust load applications or any otherbearing configuration suitable, as would be understood by one ofordinary skill in the art.

The embodiment further includes a squeeze film damper housing 60. Thehousing 60 includes a second outer surface 70 and a second inner surface80. The second inner surface 80 of the housing 60 is contiguous with thefirst outer surface 30 of bearing outer race 20. An annular channel 90for flowing a fluid is defined within the housing 60 along second innersurface 80, the channel 90 bordered by the first outer surface 30 ofbearing outer race 20. Channel 90 further includes a forward end 100 andan aft end 110.

As best seen in FIG. 2, the magnetic squeeze film damper system of thepresent embodiment further includes a first seal gland 120 located alongthe forward end 100 of channel 90. The first seal gland 120 seals theforward end 100 of channel 90. The present embodiment also includes asecond seal gland 130 located along the aft end 110 of channel 90. Thesecond seal gland 130 seals the aft end 110 of channel 90. The squeezefilm damper system, as thus far described, is configured, asconventional in the art, to provide fluid flow in the channel 90 betweenthe static structure and the shaft bearing assembly 10.

In one aspect of the present disclosure, the first seal gland 120comprises a reservoir 140 encased by an elastomer 160. The selection ofthe elastomer will be apparent to one of ordinary skill based on theparticular conditions that the elastomer will be subjected to for aparticular engine. Such particular conditions include, for example, thetemperature range that the elastomer will experience.

The reservoir 140 contains a fluid having suspended metal particles,such as a magneto-rheological fluid 170. The second seal gland 130 alsocomprises a reservoir 150 encased by an elastomer 160. The reservoir 150also contains a fluid 170 with suspended metal particles, such as amagneto-rheological fluid. The seal glands' reservoirs 140/150, with thesuspended metal particles, are completely sealed. Further, the sealglands will have a characteristic stiffness as a result of theparticular elastomer used and the magneto-rheological fluid within thesealed reservoirs.

The present embodiment includes an electromagnet 180 arranged in closeproximity to the first seal gland 120. A single electromagnet ormultiple electromagnets fall within the scope of the present invention,with the appropriate number determined based on the requirements of thespecific engine environment as would be understood by one of ordinaryskill. Similarly, a second electromagnet 190 (or electromagnets) isarranged in close proximity to the second seal gland 130.

Once energized, the electromagnets generate a magnetic field that variesaccording to the varied current used to energize the electromagnets. Themagnetic field generated by the energized electromagnets affects thesuspended metal particles in the magneto-rheological fluid therebyaltering the viscosity of the magneto-rheological fluid. Altering theviscosity of the magneto-rheological fluid changes the stiffness of theseal glands and the stiffness of the overall SFD system in proportion tothe strength of the magnetic field. Thus, varying the strength of themagnetic field achieves controlled variable damping of shaft vibrationor damping shaft axial and/or radial movement to acceptable levels. Suchvaried control is not currently feasible with standard SFD systems.

The magnetic squeeze film damper is suitable for use with anyconfiguration of gas turbine engine, including single shaft and multipleshaft versions. Referring now to FIG. 3, a cross section of a twin spool(two shaft) turbofan gas turbine engine 200 is shown. Gas turbine engine200 comprises a low pressure spool and a high pressure spool. The lowpressure spool includes fan 210, which is the first stage of lowpressure compressor 220 and a low pressure turbine 260. The low pressurecompressor 220 is connected to the low pressure turbine 260 by an innershaft 270, which rotates about a centerline 280 of gas turbine engine200.

The high pressure spool is located between the low pressure compressor220 and the low pressure turbine 260. It includes a high pressurecompressor 290 connected to a high pressure turbine 300 by outer shaft310. Outer shaft 310 also rotates about centerline 280, but rotatesindependently from inner shaft 270. Combustors 320 are located betweenhigh pressure compressor 290 and high pressure turbine 300. The highpressure compressor 290, combustors 320 and high pressure turbine 300make up the engine core 330 of gas turbine engine 200. The magneticsqueeze film damper system of the present invention can be located atany point along the shafts 270/310 of gas turbine engine 200 wherebearings are located to support said shafts. Location 340 in FIG. 3 isbut one example of a suitable location for a magnetic squeeze filmdamper system.

Referring now to FIG. 4, a three spool (three shaft) gas turbine engineis shown as another configuration of gas turbine engine where themagnetic squeeze film damper system may be used. Gas turbine engine 400includes fan 410 connected to low pressure turbine 500 by inner shaft510. Inner shaft 510 rotates about engine centerline 405. The fan 410,low pressure turbine 500 and inner shaft 510 comprise the low pressurespool.

The intermediate spool is located between the fan 410 and the lowpressure turbine 500. It includes intermediate pressure compressor 420and intermediate pressure turbine 480, which are connected byintermediate shaft 520. Intermediate shaft 520 is rotatable aboutcenterline 405 and rotates independently from inner shaft 510.

The high pressure spool is located between the intermediate pressurecompressor 420 and the intermediate pressure turbine 480. It includesthe high pressure compressor 430 and the high pressure turbine 460. Thehigh pressure compressor 430 is connected to the high pressure turbine460 by outer shaft 530. Outer shaft 530 is rotatable about centerline405 and is independent of inner shaft 510 and intermediate shaft 520.

The magnetic squeeze film damper system of the present invention can belocated at any point along the coaxial shafts 510/520/530 of gas turbineengine 400 where bearings are located to support said shafts. Location540 in FIG. 4 is but one example of a suitable location for a magneticsqueeze film damper system for the three spool gas turbine engine 400.

An electronic control system, which may include a current generator andvarious sensors, is provided to generate varied current to energize theelectromagnets and produce a varied magnetic field in proportion to thecurrent. Referring now to FIG. 5, one potential embodiment of a controlsystem 600 may include one or more speed sensors 610 connected to anelectronic control unit (ECU) 620. The ECU 620 is also connected to andcontrols the output of a current generator 630. The current generator isconnected to the at least one electromagnets 180/190. The electroniccontrol system 600 also includes power source (not shown).

In operation, the ECU 620 monitors the one or more speed sensor(s) 610.As the engine shaft reaches known modes of a super critical shaft speed,the ECU 620 receives a corresponding signal from the one or more speedsensor(s) and sends a corresponding command to the current generator630. In response to the command of the ECU 620, current generator 630generates the appropriate current to energize the at least oneelectromagnet 180/190 to produce the electromagnetic field strengthnecessary to effect the appropriate viscosity change in themagneto-rheological fluid to alter the stiffness of the seal glands,thus providing the required damping as the shaft passes through a supercritical mode.

In another embodiment, the control system may also include a g-forcetype sensor to monitor the g-forces experienced by the aircraft. Whenthe aircraft is subjected to extreme g-forces, such as when the aircraftis in a high g-force maneuver, the high g-forces could push the turbinerotor off center. In this embodiment, the ECU would recognize when theaircraft was in a high g-force maneuver via a signal from the one ormore g-force sensors. The ECU will send a corresponding command to thecurrent generator to generate the appropriate current to energize the atleast one electromagnet to produce the appropriate magnetic field toadjust the viscosity of the magneto-rheological fluid to increase thebearing system stiffness; thereby, limiting radial displacement of theturbine rotor attached to the shaft system.

Note, the scope of the control system is not limited by the examples setforth herein. One of ordinary skill in the art would understand thatmany variations of a control system are suitable and would depend on theparticular application of the invention to a particular engineconfiguration. For example, the scope of the present disclosure includescontrol systems utilizing more than one type of sensor for anyparticular application as would be understood by one of ordinary skill.Sensors, such as speed sensors, g-force sensors and gap measuringsensors can be used individually or in combination as appropriate.

In operation, the magnetic squeeze film damper system provides variablecontrolled damping that supplements the damping capabilities of the SFDalone. This supplementation will most notably occur during transientoperating conditions, such as operating through shaft critical speeds.Moreover, the additional damping capabilities of the magnetic squeezefilm damper provide additional controlled variable damping duringconditions of excessive levels of steady state synchronous vibration.

It should be understood that relative positional terms such as “aft” and“forward” and the like are with reference to the normal operationalattitude of the vehicle in which the gas turbine engine is installed andshould not be considered otherwise limiting.

The present invention has been described in an illustrative manner. Itis to be understood that the terminology that has been employed hereinis intended to be in the nature of words of description rather than wordof limitation. While there have been described herein, what areconsidered to be preferred and exemplary embodiments of the presentinvention, other modifications of the invention shall be apparent tothose skilled in the art from the teachings herein and, it is,therefore, desired to be secured in the appended claims all suchmodification as fall within the true spirit and scope of the invention.

We claim:
 1. A magnetic squeeze film damper system comprising: a bearingassembly having an outer race with a first outer surface and a firstinner surface; at least one bearing located along the first innersurface; a squeeze film damper housing having a second outer surface anda second inner surface, the second inner surface contiguous with thefirst outer surface; a channel for flowing a fluid, the channel definedwithin the squeeze film damper housing at the second inner surfacebetween the squeeze film damper housing and the first outer surface ofthe outer race, the channel having a forward end and an aft end; a firstseal gland disposed between the squeeze film damper housing and theouter race for sealing the channel forward end and a second seal glanddisposed between the squeeze film damper housing and the outer race forsealing the channel aft end; the first seal gland comprising a sealedreservoir surrounded by an elastomer, the reservoir containing amagneto-rheological fluid; and an electromagnet arranged in closeproximity to the first seal gland, whereby when the electromagnet isenergized the viscosity of the rheological fluid is varied such that thestiffness of the first seal gland is altered.
 2. The magnetic squeezefilm damper system of claim 1 wherein the fluid is engine oil.
 3. Themagnetic squeeze film damper system of claim 1 further comprising asecond seal gland having a reservoir surrounded by an elastomer, thereservoir containing a magneto-rheological fluid and a secondelectromagnet arranged in close proximity to the second seal glandwhereby when the second electromagnet is energized the viscosity of therheological fluid is varied such that stiffness of the second seal glandis altered.
 4. The magnetic squeeze film damper system of claim 1wherein the at least one bearing comprises at least one roller bearing.5. The magnetic squeeze film damper system of claim 1 wherein the atleast one bearing comprises at least one thrust bearing.
 6. The magneticsqueeze film damper system of claim 3 further comprising an electroniccontrol system operable to provide a variable current to theelectromagnet such that the viscosity of the magneto-rheological fluidis altered as a function of the variable current.
 7. The magneticsqueeze film damper system of claim 6 wherein the electronic controlsystem includes at least one sensor selected from a group of sensorscomprising a g-force sensor and a gap measuring sensor. for sensingspeed of a rotating shaft.
 8. A gas turbine engine comprising: alow-pressure compressor; an engine core located aft of the low-pressurecompressor; a low-pressure turbine located aft of the engine core; atleast one shaft rotatable around a centerline of the engine core; atleast one bearing assembly mounted to support the at least one shaft;the bearing assembly comprising an outer race with a first outer surfaceand a first inner surface; at least one bearing located along the firstinner surface; a squeeze film damper housing having a second outersurface and a second inner surface, the second inner surface contiguouswith the first outer surface; a channel for flowing a fluid, the channeldefined within the squeeze film damper housing along the second innersurface and bordered by the first outer surface, the channel having aforward end and an aft end; a first seal gland for sealing the channelforward end and a second seal gland for sealing the channel aft end; thefirst seal gland and the second seal gland each comprising a sealedreservoir surrounded by an elastomer, the sealed reservoir containing amagneto-rheological fluid; and an electromagnet arranged in closeproximity to the first seal gland, whereby when the electromagnet isenergized the viscosity of the rheological fluid is varied such that thestiffness of the first seal gland is altered.
 9. The gas turbine engineof claim 8 wherein the fluid is engine oil.
 10. The gas turbine engineof claim 8 further comprising an electronic control system operable toprovide a variable current to the electromagnet such that the viscosityof the magneto-rheological fluid is altered as a function of thevariable current.
 11. The gas turbine engine of claim 8 wherein the atleast one bearing is at least one roller bearing.
 12. The gas turbineengine of claim 8 wherein the at least one bearing is at least one ballbearing.
 13. The gas turbine engine of claim 10 wherein a secondelectromagnet is arranged in close proximity to the second seal gland,and wherein the electronic control provides a current to the secondelectromagnet for altering the viscosity of the magneto-rheologicalfluid in the second seal gland.
 14. The gas turbine engine of claim 13wherein the electronic control system includes at least one sensorselected from a group of sensors comprising a speed sensor, g-forcesensor and a gap measuring sensor. speed of the shaft.
 15. An improvedvibration damper system in combination with a gas turbine engine, thecombination comprising: a gas turbine engine comprising and engine casesurrounding a low-pressure compressor, an engine core and a low-pressureturbine, at least one shaft rotatable around a centerline of the enginecore and at least one bearing assembly for supporting the at least oneshaft; and a magnetic squeeze film damper system arranged in closeproximity to the at least one bearing assembly, the magnetic squeezefilm damper system comprising a housing, an annular channel forenclosing flowing engine oil, the annular channel defined within thehousing along an inner surface of the housing and bordered by an outerrace of the at least one bearing assembly, the annular channel furthercomprising a forward end and an aft end, the magnetic squeeze filmdamper further comprising a first seal gland and a second seal glandeach comprising a reservoir surrounded by an elastomer, the reservoircontaining a magneto-rheological fluid, the first seal gland forming aseal for the forward end and the second seal gland forming a seal forthe aft end, an electromagnet arranged in close proximity to the firstseal gland and an electromagnet arranged in close proximity to thesecond seal gland.
 16. The combination of claim 15 wherein the magneticsqueeze film damper system further includes an electronic control systemfor suppling current to the electromagnets such that when the current isvaried the stiffness of the seal glands are altered in proportion to thestrength of the current.
 17. The combination of claim 15 wherein the atleast one bearing comprises a roller bearing.
 18. The combination ofclaim 15 wherein the at least one bearing comprises a ball bearing. 19.The combination of claim 16 wherein the electronic control systemfurther includes an electronic control unit connected to a currentgenerator and to at least one sensor, the current generator furtherconnected to the electromagnets wherein a signal from the at least onesensor prompts the electronic control unit to command the currentgenerator to send a current to the electromagnets to produce a magneticfield proportional to the current.
 20. The combination of claim 19wherein the at least one sensor is selected from a group of sensorscomprising a g-force sensor and a gap measuring sensor.